Almost all radio systems receive a signal at one frequency and then convert the signal to an intermediate or baseband frequency. The radio system then demodulates the signal on the intermediate (baseband) frequency. Such radio systems require this step so that they can receive signals on a range of frequencies, but only need to demodulate the signal on one (intermediate) frequency, rather than having to demodulate the signal on each of the frequencies in the range. To convert the signal, a locally-generated intermediate frequency signal is mixed with the incoming radio frequency signal and then the resultant signal is filtered to remove all frequencies except for the signal on the intermediate frequency. This signal is then demodulated. A crystal oscillator in the receiver generates this intermediate frequency. When a complex signal that requires precise demodulation is received (such as those in wireless transceivers), the frequency reference must be very accurate so that the demodulator can recover the content cleanly.
A transceiver in current mobile stations requires a very precise intermediate frequency oscillator in order to provide a frequency reference that does not add distortion to the signal. Hence, mobile stations employ expensive, temperature-compensated crystal oscillators. There is a trade-off between the expense of precise oscillators and the degree of distortion that may be acceptable.
The present invention is directed toward overcoming one or more of the problems set forth above.